Diesel emission fluid is used in conjunction with a selective catalytic reduction catalyst to reduce oxides of nitrogen in the exhaust of the vehicle. The diesel emission fluid is stored in a tank disposed on the vehicle. The tank may include three discrete level sensors to determine the level of diesel emission fluid in the tank, i.e., the mass of the diesel emission fluid remaining in the tank. Additionally, the discrete level sensors may be utilized for refill detection when new diesel emission fluid is added to the tank. When the diesel emission fluid is thawed, i.e., in a liquid state, the vehicle operates in a non-frozen diesel emission fluid protocol. When in the non-frozen diesel emission fluid protocol, the mass of the diesel emission fluid is calculated by an algorithm, i.e., software, that evaluates the level of the diesel emission fluid in the tank based upon filtered signals from the three discrete level sensors. However, the diesel emission fluid must slosh around in the tank in order for the mass determination of the diesel emission fluid to function properly. Accordingly, if the diesel emission fluid is frozen and does not slosh around in the tank, the mass determination of the diesel emission fluid is not accurate, and does not accurately reflect the level and/or mass of the diesel emission fluid in the tank. Additionally, when the diesel emission fluid is in the frozen state, the discrete level sensors may not function and will not recognize that the diesel emission fluid is at or above the discrete level sensors.
The diesel emission fluid freezes at approximately negative eleven degrees Celsius (−11° C.). The tank includes a heater that keeps the diesel emission fluid thawed, or to thaw the diesel emission fluid when frozen. However, under certain ambient conditions, the diesel emission fluid may still freeze.
If the level and/or mass of the diesel emission fluid in the tank falls below a pre-determined level when considering the average consumption rate of the diesel emission fluid by the vehicle, the vehicle may be restricted to operation in a low diesel emission fluid inducement protocol. When operating the low diesel emission fluid inducement protocol, the speed of the vehicle is restricted to induce an operator of the vehicle to refill the tank. Once the software determines that the tank has been refilled with the diesel emission fluid, the vehicle discontinues the low diesel emission fluid inducement protocol, and is permitted to operate as normal. However, if the diesel emission fluid freezes before the refill of the tank is detected, the vehicle may continue to be restricted to the low diesel emission fluid inducement protocol.